Interaction of copper(II) with ditopic pyridyl-β-diketone ligands: Dimeric, framework, and metallogel structures

Article abstract of DOI:10.1021/cg101629w

The interaction of Cu(II) with three β-diketone ligands of type R ¹C(O)CH₂C(O)R² (where R¹ = 2-, 3-, or 4-pyridyl and R² = C₆H₅, respectively), HL¹-HL³, alo

Full text of DOI:10.1021/cg101629w

ARTICLE
pubs.acs.org/crystal
Interaction of Copper(II) with Ditopic Pyridyl-β-diketone
Ligands: Dimeric, Framework, and Metallogel Structures
Melanie Dudek,† Jack K. Clegg,‡ Christopher R. K. Glasson,§ Norman Kelly,† Kerstin Gloe,† Karsten Gloe,*,†
Alexandra Kelling,|| Hans-J€urgen Buschmann,^ Katrina A. Jolliffe,‡ Leonard F. Lindoy,*,‡ and
George V. Meehan§
†Department of Chemistry and Food Chemistry, TU Dresden, 01062 Dresden, Germany
‡School of Chemistry, University of Sydney, NSW 2006, Australia
§School of Pharmacy and Molecular Sciences, James Cook University, Townsville 4811 Queensland, Australia
Institute of Chemistry, University of Potsdam, 14469 Potsdam, Germany
^German Textile Research Centre DTNW, 47798 Krefeld, Germany
S Supporting Information
b
ABSTRACT: The interaction of Cu(II) with three β-diketone
ligands of type R1C(O)CH2C(O)R2 (where R1 = 2-, 3-, or
4-pyridyl and R2 = C6H5, respectively), HL1-HL3, along with
the X-ray structures and the pKa values of each ligand, are
reported. HL1 yields a dimeric complex of type [Cu(L1)2]2. In
this structure, two deprotonated HL1 ligands coordinate in a trans
planar fashion around each Cu(II) center, one oxygen from each
CuL2 unit bridges to an axial site of the second complex unit such
that both Cu(II) centers attain equivalent five-coordinate square
pyramidal geometries. The two-substituted pyridyl groups in this
complex do not coordinate, perhaps reflecting steric factors
associated with the closeness of the pyridyl nitrogen to the
attached (conjugated) β-diketonato backbone of each ligand.
The remaining two Cu(II) species, derived from HL2 and HL3,
are both coordination polymers of type [Cu(L)2]n in which the
terminal pyridine group of each ligand is intermolecularly linked
to an adjacent copper center to generate the respective infinite
structures. HL2 was also demonstrated to form a fibrous metallogel when reacted with CuCl2 in an acetonitrile/water mixture under
defined conditions.
’ INTRODUCTION
generation of a range of interesting coordination polymers. In
these hetero difunctional ligand systems, the β-diketone frag-
ment has the pyridyl substituent attached either to the “central”
carbon atom (that is, the carbon between the two keto functions)
or in a terminal position with respect to this fragment. Thus, the
linear bifunctional derivative, 3-(4-pyridyl)pentane-2,4-dione,
has been demonstrated to be an effective ligand for generating
a number of one- (1D) and two-dimensional (2D) coordination
polymers incorporating a range of metal ions;20-24 linear poly-
meric, ladder, and square-grid architectures have all been ob-
served. A corresponding nonlinear ligand in which the pyridyl
group is coupled to a β-diketone fragment via a “bent” thioether
linkage has also been demonstrated to yield porous 2D and three-
The synthesis of new metal coordination polymers, including
new metal organic frameworks, has been given increasing atten-
tion over recent years, in part motivated by their ready prepara-
tion via self-assembly processes and by the prospect of generating
new materials exhibiting useful and/or unusual properties.1-11
Thus, systems showing luminescent,12-14 nonlinear optical,15
catalytic,16 magnetic spin-crossover,17,18 as well as other less
common magnetic properties19 have all been documented.
Linear difunctional ligand systems (such as, for example, 4,40-
bipyridyl or terephthalic acid) have very commonly been em-
ployed to connect metal units in the formation of such materials,
while nonlinear bifunctional ligands have received somewhat less
attention. Nevertheless, both categories have now been demon-
strated to form a range of diverse metallo-polymeric structures.
For example, both linear and nonlinear, pyridyl-substituted
β-diketonato ligands have been successfully employed for the
Received: December 8, 2010
Revised:
February 9, 2011
Published: March 10, 2011
r
2011 American Chemical Society
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dimensional (3D) networks with Cu(II) and Zn(II).25 In other
studies, a number of pyridyl terminally substituted difunctional
β-diketone derivatives have also been used to form both homo-
and heteronuclear coordination polymers.20,26,27 It is clear that
both of the above categories of ligand, each of which contains
“classical” pyridyl and β-diketonato metal binding motifs, are
extremely versatile systems for generation of metal coordination
polymers displaying diverse architectures. These interesting
structural arrangements have, in part, provided a motivation
for undertaking the present investigation.
Finally, it is noted that pyridine has been shown to react with
Cu(II) β-diketonates to form corresponding pyridine adducts,28
and a related two step synthetic procedure involving Cu(II)
complexes of dibenzoyl- or benzoylacetyl methane and a bifunc-
tional heterocyclic amine ligand has been employed to produce a
range of corresponding metallo-frameworks.29-31
We now report the results of a structural study of the three
isomeric ligands HL1-HL3 and their complexes with Cu(II).
While these diketo derivatives were first reported almost 60 years
ago32 and some preliminary results on their Cu(II) complexation
were discussed in the 1960s,33 since then only two reports have
been published on metal complexation by such systems [des-
cribing structural details of mixed valent Mn(II)/Mn(III) tetra-
and hexanuclear manganese cluster complexes with HL1 that
show interesting magnetic properties];34,35 a recent further
publication has appeared relating to the antimicrobial activity
of uncomplexed HL1 and HL2.36
Figure 1. X-ray structures of (a) HL1, (b) HL2, and (c) HL3 showing
the intramolecular hydrogen bonds.
1H), 7.98 (br s, -CH- enol, 1H), 7.69 (t, aromatic, 1H), 7.59 (t, aromatic,
1H), 7.52 ppm (t, aromatic, 1H). ESI-MS: m/z 226.0 (M þ H)þ.
1-Phenyl-3-(3-pyridyl)-1,3-propandione (HL2). This was pre-
pared as a pale yellow solid from sodium amide (0.79 g, 20 mmol),
methyl nicotinate (1.401 g, 10 mmol), and acetophenone (2.568 g,
21 mmol) in THF (42 mL). Yield, 1.72 g (7.66 mmol, 77%). 1H NMR δ
(300 MHz CDCl3): 16.71 (br s, enol, 1H), 9.20 (br s, aromatic, 1H),
8.78 (d, aromatic, 1H), 8.27 (dd, aromatic, 1H), 8.01 (d, aromatic, 2H),
7.59 (t, aromatic, 1H), 7.52 (t, aromatic, 2H), 7.45 (t, aromatic, 1H),
6.87 ppm (s, -CH- enol, 1H). ESI-MS: m/z 226.0 (M þ H)þ.
1-Phenyl-3-(4-pyridyl)-1,3-propandione (HL3). This was pre-
pared as a pale yellow solid from sodium amide (0.49 g, 12 mmol),
methyl isonicotinate (0.622 g, 5 mmol), and acetophenone (1.358 g, 11
mmol) in 25 mL of THF. Yield, 0.826 g (3.667 mmol, 73%). 1H NMR δ
(500 MHz CDCl3): 16.34 (br s, enol, 1H), 8.92 (br d, aromatic, 2H),
8.37 (d, aromatic, 2H), 8.04 (d, aromatic, 2H), 7.67 (t, aromatic, 1H),
7.55 (t, aromatic, 2H), 7.03 ppm (s, -CH- enol, 1H). ESI-MS: m/z
226.0 (M þ H)þ.
’ EXPERIMENTAL SECTION
Materials and Methods. All reagents and solvents were pur-
chased from commercial sources and used without purification with the
exception of tetrahydrofuran (THF), which was dried over sodium wire
before use. NMR spectra were recorded on a Bruker DRX500 spectro-
meter, and HRMS were determined using a Bruker ESQUIRE mass
spectrometer. Elemental analyses were performed on a vario Micro
Cube analyzer.
General Preparation of HL1-HL3. These were prepared by a
modification of the procedure reported by Levine and Sneed.31 The
required methylester and acetophenone (see below) in dry THF were
added to a suspension of sodium amide in dry THF at room tempera-
ture. The reaction mixture was refluxed for 6 h over which time the
mixture turned brown. The reaction was quenched with acetic acid and
water (40 mL), and the organic (THF) and aqueous phases were
separated. The aqueous phase was washed three times with diethylether
(40 mL), and the organic phases were combined and dried over
anhydrous sodium sulfate. The solvent was removed under reduced
pressure to yield the crude product, which was purified by column
chromatography employing silica gel. Yields and characterization details
for each product are given below.
Complex Synthesis. Synthesis of [Cu(L1)2]2.HL1 (50 mg, 0.22 mmol)
in dry THF (10 mL) was added to Na2CO3 (0.5 g, ∼5 mmol) suspended in
dry THF (15 mL). The mixture was stirred for 1 h before Cu(NO3)2 3H2O
3
(26.58 mg, 0.11 mmol) in THF (15 mL) was added dropwise, and the
mixture was stirred at 35 ꢀC for 2 h. Diffusion of a diethylether-hexane
mixture (1/1, v/v) into the green solution yielded green needles after a few
days. Found: C, 65.84; H, 4.48; N, 4.93%. Calcd for C28H20CuN2O4: C,
65.68; H, 3.94; N, 5.47%. ESI-MS: m/z 512.1 [Cu(L1)2 þ H]þ.
Synthesis of [Cu(L2)2]n. HL2 (100.3 mg, 0.45 mmol) in dry THF
(10 mL) was added to Na2CO3 (0.51 g, ∼5 mmol) suspended in dry
1-Phenyl-3-(2-pyridyl)-1,3-propandione (HL1). This was pre-
pared as a yellow solid from sodium amide (0.895 g, 23 mmol), methyl
picolinate (1.238 g, 10 mmol), and acetophenone (2.41 g, 20 mmol) in
THF (42 mL). Yield, 1.56 g (6.94 mmol, 69%). Found: C, 74.41; H,
5.44; N, 5.91. Calcd for C14H11NO2: C, 74.65; H, 4.92; N, 6.22%. 1H
NMR δ (500 MHz CDCl3): 16.42 (br s, enol, 1H), 8.84 (d, aromatic,
1H), 8.33 (d, aromatic, 1H), 8.21 (d, aromatic, 2H), 8.15 (t, aromatic,
THF (5 mL). This mixture was stirred for 1 h before CuCl2 2H2O
3
(38.8 mg, 0.23 mmol) in THF (15 mL) was added dropwise, and stirring
was continued at room temperature for 2 h. Slow evaporation of a small
amount of this solution over 24 h yielded a green crystalline product,
which was isolated and washed with THF. Found: C, 66.05; H, 4.05; N,
5.58%. Calcd for C28H20CuN2O4: C, 65.68; H, 3.94; N, 5.47%. ESI-MS:
m/z 512.1 [Cu(L2)2 þ H]þ.
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Figure 2. (a) ORTEP representation of the asymmetric unit of [Cu(L1)2]2. (b) ORTEP representation of the dinuclear dimer of [Cu(L1)2]2, shown
with 50% probability ellipsoids.
Figure 3. (a) π-π interactions within the [Cu(L1)2]2 dimers and (b) Cu(II)-π interactions between the dimer units and (c) the 3D structure of
[Cu(L1)2]2.
Synthesis of [Cu(L3)2]n. HL3 (50 mg, 0.22 mmol) in dry THF
(5 mL) was added to Na2CO3 (0.5 g, ∼5 mmol) suspended in THF
65.86; H, 4.29; N, 5.29%. Calcd for C28H20CuN2O4: C, 65.68; H, 3.94;
N, 5.47%. ESI-MS: m/z 512.1 [Cu(L3)2 þ H]þ.
(15 mL). This mixture was stirred for 1 h before Cu(NO3)2 3H2O
Metallogel Preparation and Characterization. For investi-
gating metallogel formation, solutions of ligand HL2 (0.2 mmol,
3
(26.6 mg, 0.11 mmol) in THF (15 mL) was added dropwise. The
solution was warmed to 35 ꢀC, and stirring was continued for 2 h.
Diffusion of a diethylether-hexane-mixture (1/1, v/v) into the green
solution yielded green cuboidal crystals after several days. Found: C,
45.05 mg) and CuCl2 2H2O (0.2 mmol, 34.11 mg) in 20 mL of an
3
acetonitrile/water mixture (v/v 1:1) were prepared and mixed in varying
mole fractions (x) between x (ligand) = 0.1 and 0.9. Gelation was
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Figure 4. (a) ORTEP representation of the asymmetric unit of Cu(1)(L2)2, shown with 50% probability ellipsoids, and (b) the connection between
individual chelate units. Regions of disorder are removed for clarity. N1 coordinates to Cu2, and N2 remains uncoordinated.
obtained immediately in the samples for mole fractions between x
(ligand) = 0.2-0.6. SEM analyses were undertaken on xerogel samples
with an average thickness of 4-6 mm formed by evaporation of the gel
to dryness under vacuum at 120ꢀ for 6 h. Sample preparation involved
placing a dry amount of gel on carbon-coated grids and sputtering with a
Au/Pd alloy. Cryogel samples were obtained by freezing the gel samples
at -20ꢀ. The overlaying solvent was removed, and the samples were
evaporated to dryness at -10ꢀ and 0.370 mbar overnight using a freeze
dryer. Sample preparation involved placing a dried amount of gel on
grids, coating with silver lacquer, and then sputtering with a Au/Pd alloy.
Images were obtained using a DSM 982 Gemini (Zeiss) and accelerating
voltage of 3 and 5 kV.
’ RESULTS AND DISCUSSION
Ligand X-ray Structures and pKa Values. The X-ray struc-
tures of HL1-HL3 are illustrated in Figure 1a-c. As is normal for
such systems, in each case, the β-diketone fragment is in its enol
form. Interestingly, the enolic proton is attached to O1, the
oxygen adjacent to the terminal aryl ring in the case of HL1, but in
HL2 and HL3, it is adjacent to the 3- or 4-pyridyl group, probably
reflecting the near electronic equivalence of these two aromatic
ring types in relation to the attached β-diketone fragment.
All three structures reveal the presence of the expected strong
resonance-assisted intramolecular hydrogen bond37 involving
Figure 5. Schematic representation of a part of one of the lattice layers
present in [Cu(L2)2]n. Both disordered positions of Cu2 are shown.
O1-H O2. For example, the O1-H100 O2 distance in
3 3 3 3 3 3
HL1 is 1.398 Å, and the angle is 157.7ꢀ. Weaker intramolecular C-
O1 (O2) and C-H N hydrogen bonds38 together with
X-ray Structures of Cu(II) Complexes. Dimeric [Cu(L1)2]2
and polymeric [Cu(L2)2]n and [Cu(L3)2]n complexes were
formed by reaction of Cu(NO3)2 3H2O or CuCl2 2H2O
H
3 3 3
3 3 3
weak intermolecular hydrogen bonds and π-π interactions are
also evident in each case, leading to 3D packing arrangements in the
crystal structures of these ligands (see the Supporting Information).
The pKa values of the β-diketone ligands were determined
potentiometrically in an ethanol/water mixture (2:1 v/v) and
show the expected weak acidic character of the ligands. The
values increase in the order HL3 (7.66 ( 0.02) < HL2 (8.16 (
0.05) < HL1 (8.40 ( 0.01), with the values for HL1 and HL2
being slightly higher than the corresponding constants in water.39
3
3
with 2 equiv of the respective ligands in THF in the pres-
ence of a stirred suspension of sodium carbonate as base.
Green crystals suitable for X-ray analysis were obtained
by slow diffusion or direct crystallization from the reaction
solution. In the case of HL2, an identical complex could
be also isolated from an acetonitrile-water mixture without
addition of base.
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Figure 6. (a) ORTEP representation of the asymmetric unit of [Cu(L3)2]n and (b) ORTEP representation of the connection of alternate copper
centers, shown with 50% probability ellipsoids.
The structure of [Cu(L1)2]2 (Figure 2a) shows that two
deprotonated HL1 ligands coordinate in a trans planar fashion
around each central copper ion, with all four Cu-O distances
being essentially equal at 1.91-1.92 Å. The structure (Figure 2b)
is a dinuclear dimer in which one oxygen from each monomeric
complex unit bridges to an axial site of the second complex unit and
vice versa such that each metal center in the dimer attains an
equivalent five-coordinate square pyramidal geometry (τ = 0.09).40
The Cu-Cu distance in each dimer is 3.3 Å, and the axial (bridging)
Cu-O bonds (namely, Cu-O7A0 and Cu0-O7A) are Jahn-Teller
elongated at 2.69 Å, with the O7A-Cu-O7A0 angle being 89.3ꢀ.
The terminal 2-pyridyl groups of each coordinated ligand are
not bound, perhaps reflecting steric factors associated with the
closeness of the 2-pyridyl nitrogen donor to the remainder of
the ligand backbone. Individual pyridyl groups and phenyl rings
lie opposite each other within each dimer unit (Figure 3a). The
centroid-centroid distances are 4.03 and 4.11 Å, suggesting that
marginal π-π interactions may be present between opposing
rings. The offset arrangement between successive dimeric units is
shown in Figure 3b. Each Cu(II) center is located 3.6 Å from the
centroid of a pyridyl ring present in an adjacent dimer unit, in
accordance with the presence of weak “axial” interactions bet-
ween the copper centers and the π-systems of these rings.41-48
When viewed from off the c-crystallographic axis the zigzag
pattern formed by adjacent columns is illustrated in Figure 3c.
No other significant intermolecular interactions are present
between dimer units.
The structure of [Cu(L2)2]n shows the presence of two
nonequivalent copper centers, Cu1 and Cu2, with the latter
being disordered over two positions (across an inversion center)
with 50% occupancy in each case (Figure 4). Each of the copper
centers is five-coordinated, with four oxygen donors occupying
the basal plane and a pyridyl donor occupying the apical position
resulting in square-pyramidal coordination geometry. Interest-
ingly, the N2-containing pyridyl ring is not involved in the Cu(II)
coordination but participates in the formation of an additional
weak hydrogen bond to the phenyl ring of the neighboring layer
(CH N2 = 2.65 Å), strengthening the network arrangement.
3 3 3
The structure forms an infinite 2D lattice. If Cu1(L2)2 is
considered a two-connecting node and the Cu2(L2)2 fragment is
considered a four-connecting node, then, overall, the structure
can be described effectively as a distorted (4,4)-network49
(Figure 5).
Because of the disorder present in the Cu2 site, however, there
are a large number of randomly distributed disruptions in the
lattice structure (that is, ∼50% of the Cu2-N3 bonds illustrated
in Figure 6 are absent). Adjacent layers pack closely together with
a number of π-π interactions (showing both face-to-face and
edge-to-face orientations) being present between the layers.
The molecular structure of [Cu(L3)2]n is shown in Figure 6a.
In analogy with the structures discussed above, the two depro-
tonated HL3 ligands adopt a trans planar arrangement around
one copper ion with Cu-O distances of ∼1.95 Å.
At alternate copper centers, the structure is extended in a
second direction at approximately right angles to generate a
layer arrangement (Figure 6b), incorporating slightly rhom-
boidal cavities (angles: O7A-Cu-N3A, 95.0ꢀ; O7B-Cu-
N3B, 98.3ꢀ; O7A-Cu-N3B, 82.5ꢀ; and O7A-Cu-N3A,
95.0ꢀ) with the copper ions defining the corners of each
rhombus (Figure 7).
A variable temperature magnetic investigation of [Cu(L1)2]2
has been undertaken. No magnetic exchange between the copper
centers in the dimer units was observed, undoubtedly reflecting
the extended distance (3.3 Å) between these centers and the
elongated Jahn-Teller distortion present in the O7A-Cu
bridges (2.69 Å).
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into the space between successive layer pairs. Reflecting the
smaller size of the terminal methyl groups (relative to the phenyl
groups in HL3), solvent methanol molecules also occupy this
space in this case.
Metallogel Formation with HL2. While studying the com-
plexation properties of HL2 toward Cu(II), metallogel formation
was observed in an acetonitrile-water mixture (v/v 1:1) for
mole fractions (x) of HL2 between 0.2 and 0.6 in the presence of
CuCl2 (Figure 9). HL2 was not observed to form a gel by itself
under a range of experimental conditions; also, the use of
Cu(NO3)2 or Cu(CH3COO)2 as copper salts does not lead to
metallogel formation. Gelation was easily initiated by mixing the
respective solutions without the addition of a separate base.
Obviously, the pyridine substituent of HL2 promotes the proton
abstraction in this case. The product gels are stable at room
temperature, but their formation can be reversed by shaking.
Over recent years, metallogels based on various ligand types
have attracted increasing interest due to their potential for use in
a number of application options.50-55 To the best of our know-
ledge, the present system is the first example of a low molecular
weight gelator based on a metal-coordinated simple β-diketone
skeleton. In this context, we are only aware of gel formation by
the Cu(II) β-diketonate of dibenzoyl methane substituted by
eight C9H19O functions56 and an alkyl chain-appended bis-
β-diketone compound incorporating a diaminocyclohexane plat-
form. This later gel can be strengthened by the addition of
Co(II), Ni(II), or Cu(II).57
Figure 7. 2D lattice structure of [Cu(L3)2]n showing the rhomboidal
cavities.
The above copper-containing gel was investigated by scanning
electron microscopy (SEM). SEM micrographs of the dried
(xerogel) and freeze-dried (cryogel) gel obtained for HL2 at
the mole fraction x = 0.5 alongside the packing motif in the
corresponding single crystal of the polymeric complex [Cu-
(L2)2]n are shown in Figure 10. The gel is characterized by a
typical fibrous network, with the fibers having diameters of up to
40 nm. Such an arrangement is assumed to be mainly based on
the interplay of multiple weak interactions in the system. In this
context, analysis of the solid state structure appears to give some
preliminary insights into the observed gel formation, especially in
view of the fact that only HL2 gives gels (the two isomeric ligands
HL1 and HL3 did not form gels under comparable conditions to
that used for HL2). As shown in Figure 4, the single crystal
structure of the polymeric [Cu(L2)2]n is characterized by typical
square planar coordination of the two β-diketonato units for the
Cu(II) center in a similar manner to the other two complexes.
However, in the case of [Cu(L2)2]n, additional weak hydrogen
bonds of the uncoordinated pyridine nitrogen and multiple π-π
interactions of the aromatic fragments are present that lead to
packed extended columnar arrays. The observed diverse weak
binding pattern differs markedly from that in the two other
complexes and is manifested by very different solid state struc-
tures. By analogy, the difference in the weak interaction possibi-
lities between the above three complexes very likely plays an
important role in the gelation process. Weak interactions invol-
ving the gelator and solvent molecules have been well established
to be a decisive parameter in gel formation.
Figure 8. Layer pairs in [Cu(L3)2]n showing how the phenyl groups
occupy the intervening space between them.
Phenyl rings from an adjacent layer occupy the above rhom-
boidal cavities such that the layers are paired, and a discontinuity
is present between successive layer pairs (Figure 8). No strong
intermolecular interactions are present between the layer pairs;
however, the second phenyl group from each complex unit
points outward from these pairs, occupying the intervening space
between them.
The results of a related study by Domasevitch et al.27 are of
direct relevance to the present system. These workers reported
the structure of the Cu(II) complex of 1-(4-pyridyl)butan-1,3-
dione, the analogue of HL3 in which a methyl group replaces the
terminal phenyl ring. In this case, a related gridlike structure was
generated in which each rhomboidal cavity is occupied by a
methyl group from a neighboring complex unit; within this
system, the second methyl from each complex unit is directed
It is interesting to note that HL1 and HL3 did not form
metallogels under comparable conditions to that used for HL2. It
is likely that this difference in the ligand series can be attributed to
the changing position (from 2- and 4-position to 3-position) of
the pyridine nitrogen atom in the pyridyl substituents, leading to
different structural arrangements and, in particular, differences in
the weak intermolecular interactions linking complex units. This
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Figure 9. Vials containing an acetonitrile/water (v/v 1:1) solution of HL2 and increasing amounts of CuCl2 2H2O showing metallogel formation at
3
mole fractions (x) of HL2 between 0.2 and 0.6 after mixing.
Figure 10. Comparison of the “columnar” structure of [Cu(L2)2]n found in the crystal packing (a) and fibrous structure in the xerogel (b) and in the
cryogel (c). The latter representations are SEM micrographs of the metallogel after drying and freeze drying in vacuum at the mole fraction x = 0.5.
conclusion is supported by significant differences in the solid
state Cu(II) complex structures of the diketonates. As shown by
their X-ray structures, in comparison to [CuL1)2] and [Cu(L3)2]n,
the new gelator [Cu(L2)2]n shows additional hydrogen bonds
and π-π stacking interactions, which may contribute to stabi-
lization of the columnar structure in this case.
interaction patterns occurring between the respective complexes.
More generally, the study also illustrates that solid state structural
data can be a useful adjunct to the investigation of metallogelation
behavior of the type discussed above.
’ ASSOCIATED CONTENT
’ CONCLUSION
S
Supporting Information. X-ray crystallographic details
b
In the present study, we have synthesized and characterized
new examples of a dimeric and two polymeric metal β-diketonato
complex structures whose interesting molecular architectures
clearly reflect the presence (and availability) of additional pyridyl
functionality present on each of the β-diketone derivatives of type
HL1-HL3. Whereas the chelating binding pattern in all three
complexes is comparable, there are significant differences in the
intermolecular interactions that are present between the complex
units. Along this ligand series, only HL2 was demonstrated to form
a metallogel with CuCl2 underscoring the role of the different
pyridyl substituents in controlling the hydrogen bonding and π-π
of the ligand and Cu(II) complex structures including H-bond
and π-interaction data, selected bond lengths and angles, IR,
1H NMR and UV-vis spectroscopic data, additional figures of
the structures and information about the gel formation. The
data is also deposited in the Cambridge Crystallographic Data
Centre (CCDC), deposition numbers CCDC 814650-814652
(HL1-HL3) and CCDC 814653-814655 {[Cu(L1)2]2, [Cu
(L2)2]n, [Cu(L3)2]n}. These data can be obtained free of
charge via www.ccdc.cam.ac.uk/data_request/cif, or by email-
ing data_request@ccdc.cam.ac.uk, or by contacting The
Cambridge Crystallographic Data Centre, 12, Union Road,
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Cambridge CB2 1EZ, UK; fax: +44 1223 336033. This material is
available free of charge via the Internet at http://pubs.acs.org.
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’ AUTHOR INFORMATION
Corresponding Author
*E-mail: (K.G.) karsten.gloe@chemie.tu-dresden.de or (L.F.L.)
lindoy@chem.usyd.edu.au.
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’ ACKNOWLEDGMENT
We thank the Deutsche Forschungsgemeinschaft, the
Australian Research Council, and the IPDF Scheme
(University of Sydney) for support. M.D. acknowledges
gratefully the Deutsche Bundesstiftung Umwelt for a Ph.D.
grant. We also thank Berthold Kersting and Jochen Lach,
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